The present invention concerns an impact torque adjusting device of a hydraulic torque wrench.
Conventionally, a hydraulic torque wrench using, as a hydraulic impact torque generator of the torque wrench, a hydraulic impact torque generator with little noise and vibration has been developed and put to practical use (see Laid-open Utility Model Application No. H3-40076 and Laid-open Patent Application No. H6-297349, for example).
FIG. 6 and FIG. 7 show an example of such a hydraulic torque wrench. Here, the hydraulic torque wrench 1 comprises a main valve 2 for supplying and stopping high-pressure air, and a normal-reverse turn switching valve 3 for selectively generating impact torque of normal and reverse turns, so as to drive a rotor 4 for generating rotational torque with high-pressure air fed through those two valves 2, 3. A hydraulic impact torque generator 5 for converting the rotational torque of the rotor 4 into impact torque is provided in the case 6 of the hydraulic torque wrench 1.
The hydraulic impact torque generator 5 is constructed by charging and sealing an operating fluid in a cavity formed in a liner 7 turned by the rotor 4, providing two blade insertion grooves (there are also cases with one only or a plurality no less than 3) in a spindle 8 placed coaxially in the liner 7, inserting a blade 9 in the blade insertion grooves, and urging the blade 9 constantly in the outer circumferential direction of the spindle 8 with a spring 10 so that it may be in contact with the inner circumferential face of the liner 7.
Moreover, on the hydraulic impact torque generator 5 is disposed an output adjusting mechanism 11 to enable adjustment of the amount of the impact torque to be generated.
And, by rotatably driving the liner 7 with the rotor 4, it becomes possible to generate an impact torque on the spindle 8, to tighten or loosen a nut, etc. fastened to the tip of the spindle 8, when a plurality of sealed faces formed on the inner circumferential face of the liner 7, the sealed face formed on the inner circumferential face of the spindle 8 and the blade 9 agree with one another.
By the way, in a conventional hydraulic torque wrench, the output adjusting mechanism 11 for adjusting the amount of the impact torque to be generated is constructed in a way to discharge its function, by adjusting the size of the operating fluid channel communicating through the liner 7 which becomes a high-pressure chamber and a low-pressure chamber at the time impact torque is generated, with an operation of the operating shaft. The amount of the impact torque becomes smaller if the operating fluid channel is widened with an operation of the operating shaft to the opening side and, conversely, the amount of the impact torque becomes larger if the operating fluid channel is narrowed with an operation of the operating shaft to the closing side.
However, the size of the operating fluid channel adjusted with operations of the operating shaft remains constant (fixed) during an operation of the hydraulic torque wrench, and this presents the following problems (1)˜(4):
(1) A large error (difference) between the amount of the actually generated impact torque and the set impact torque.
(2) An unusually high impact torque is liable to be generated at the time of starting of the tightening motion (at seating of the tightening member).
(3) A large resistance after the generation of impact torque (after the generation of pulse), and long impact torque generating period.
(4) Poor durability due to a load pressure which is liable to be exerted on the sealed part.